1. Field of the Invention
This invention relates generally to foundation repair methods and apparatus, and more particularly to a foundation repair method and apparatus utilizing precast concrete cylinders joined by tubular connectors to create a column which is sequentially driven into the soil to form an underground pier.
2. Brief Description of the Prior Art
There are several conventional methods known for repairing the foundations of buildings having a slab-on-ground foundation.
One of the most common methods of foundation repair comprises the use of drilled underground piers. Holes are drilled to a depth of approximately eight to twelve feet and filled with concrete to a level of approximately twelve inches below the grade beam. The depth of the bottom of the pier is a function of the type of soil and is located below the zone of seasonal moisture change. The bearing surface of the repair pair pier is increased by a bell-shaped bottom configuration. After the concrete has dried, jacks are placed on top of the pier and the foundation is brought to a level position. Blocks, shims, and/or grout are then used to replace the jack. This poured concrete pier method is labor intensive, time consuming, and expensive.
A more recent method of repairing foundations is with the use of driven precast concrete piles. In this method, a plurality of precast solid concrete cylindrical pile members approximately one foot in length and six inches in diameter are driven into the ground one on top of the other to form a column of the stacked concrete cylinders. One or more larger diameter cylindrical concrete members and/or concrete blocks at the top of the stacked column form the pile cap. Jacks are placed on top of the pile cap and the foundation is brought to a level position. Blocks, shims, and/or grout are then used to replace the jack. The precast concrete pile method relies upon the skin friction with the soil for its strength. It has the advantage of being faster since the concrete does not have to cure and precasting allows better control of the concrete strength. A major disadvantage is that the one foot cylindrical sections may shift and become misaligned during or after the driving operation.
Another common technique of stabilizing soil beneath a foundation is to provide a partial moisture barrier by injecting a lime slurry under pressure into the soil around the edge and beneath the grade beam until the lime is rejected by the soil. The lime tends to increase the moisture content around the critical perimeter area where soil shrinkage has occurred. Although some restoration may occur, this technique does not necessarily return the foundation to its original level position.
The present invention is distinguished over the prior art in general, by a method of repairing foundations utilizing precast concrete cylinders connected by tubular connectors to create a column which is sequentially driven into the soil to form an underground pier. The tubular connectors maintain the cylindrical members in straight alignment during and after the driving operation and prevent shifting as a result of changing soil conditions. The present method relies upon the skin friction of the precast concrete pier with the soil for its strength and the precast concrete pier thus formed may be further strengthened by using hollow concrete cylinders and adding concrete or mud pumped into its center and into the surrounding soil. The soil surrounding the precast concrete pier may be further stabilized and strengthened by pumping a lime, concrete, or mud slurry through the column into the soil surrounding the pile at critical areas where soil shrinkage and shifting often occurs. The present method has the advantage of being faster since the precast concrete cylinders do not have to cure and precasting allows better control of the concrete strength.